In burner systems the air/fuel ratio during combustion is able to be established on the basis of an ionization current by an ionization electrode. First of all an AC voltage is applied to the ionization electrode. Because of the rectifier effect of a flame, an ionization current flows as a DC current in only one direction.
In regulating curves for ionization electrodes the ionization current detected at the ionization electrode is plotted against the rotational speed of the fan of a gas burner. The ionization current is typically measured in microamperes. The rotational speed of the fan of a gas burner is typically measured in revolutions per minute. The rotational speed of the fan of a gas burner is at the same time a measure for the air volume flow rate and for the power of the burner system, i.e. for a quantity of heat per unit of time.
Entered along such a regulating curve is a plurality of test points. Initially these test points can be recorded under laboratory conditions as part of testing. The recorded values are stored and taken into account in (electronic) control.
Ionization electrodes are subject to ageing during operation. This ageing is caused by deposits and/or accumulation of layers during the operation of a burner system. In particular a layer of oxide, the thickness of which changes over the hours of operation, can form on the surface of an ionization electrode. As a result of the ageing of an ionization electrode, a drift of the ionization current occurs. Thus a regulating curve recorded under laboratory conditions requires correction from time to time, at the latest after 1000 to 3000 hours of operation.
A regulation device with correction of the regulating curve of an ionization electrode is disclosed in EP2466204B1. The regulating curve is corrected here in three steps. First of all the regulation device performs regulation operation. Subsequently the regulation device controls or regulates the actuators of the burner system to a changed supply ratio. In particular the speed of the fan of a burner system is changed. By controlling the actuators the regulation device sets an air volume flow rate of the burner system.
The changed supply ratio in this case lies above the stoichiometric value of the air-fuel ratio of 1. Preferably the air-fuel ratio is reduced by 0.1 or by 0.06 to values greater than or equal to 1.05. In a third step a new required value is computed from the ionization signal detected in such cases and from stored data.
However the correction of the regulating curve requires that the heat created during the duration of the tests can also be dissipated to consumers, such as heating or process water. Otherwise the amount of heat created during the test is higher than the amount of heat dissipated. As a result the temperature in the system increases and the temperature controller of the system switches the burner off. The test on a specific air volume flow rate cannot be completed in this case.
This problem becomes even more acute because a little time is needed during a test run to obtain stable values. Another complicating factor is that the duration of a test run can generally not just be shortened arbitrarily.